Journals >Chinese Journal of Lasers
Contents
2007
Volume: 34 Issue 4
28 Article(s)
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Research Article
Laser Diode Double-End-Pumped Acousto-Optically Q-Switched Nd:GdVO4Laser with High Repetition Rate
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Laser diode (LD) pumped Q-switched solid-state lasers (SSLs) can achieve high repetition rates and high peak power. With the development of lidar and laser machining, diode-pumped SSLs (DPSSLs) with higher repetition rates are required. In the LD-end-pumped acousto-optically (A-O) Q-switched solid state lasers, Nd:GdVOLaser diode (LD) pumped Q-switched solid-state lasers (SSLs) can achieve high repetition rates and high peak power. With the development of lidar and laser machining, diode-pumped SSLs (DPSSLs) with higher repetition rates are required. In the LD-end-pumped acousto-optically (A-O) Q-switched solid state lasers, Nd:GdVO4, which has excellent physical and laser properties, is able to obtain a laser output of short pulse width even at very high repetition rates. The major factors that have influence on pulse energy and pulse width are analyzed, pulse width, average output power and peak power as a function of the repetition rates have been studied. Double Nd:GdVO4 crystals laser end-pumped by double LD is reported, and A-O Q-switched laser of 1063 nm with high repetition rate and short width is achieved. At the total pump power of 43 W, pulse width of 10.2 ns, pulse energy of 0.95 mJ and peak power of 93.1 kW are obtained at the repetition rate of 10 kHz; 28.1 ns, 0.10 mJ and 3.6 kW are produced respectively at 100 kHz..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 461 (2007)
Producing Mono-Pulse Laser of Nanosecond Burst-Length by Cutting-Apart from Q-Beam Self-Triggered
[in Chinese], [in Chinese], and [in Chinese]
For obtaining simple mono-pulse laser of nanosecond burst-length and high peak power with available equipments in order to satisfy time-resolved demands in something to do with military application and in interferometric research of high temperature plasma, the trigged gap of KDP Pockels cell for chopping Q-beam itselfFor obtaining simple mono-pulse laser of nanosecond burst-length and high peak power with available equipments in order to satisfy time-resolved demands in something to do with military application and in interferometric research of high temperature plasma, the trigged gap of KDP Pockels cell for chopping Q-beam itself was optimized by using certain patent technique, the dilemmas of dual reliability as well as synchronism of whole system were overcome in both static electric-separating of the gap enduring at full-wave voltage (Vλ) of 19 kV and easily puncturing of the insulating film between gap′s electrodes by the low front of Q-beam self-triggering, the high-speed triggering and the chopping near the peak of Q-beam were guaranteed, and a mono-pulse laser of 1.7 ns burst-length with 4 mJ pulse energy cut apart from Q-beam of a 30 ns/80 mJ traditional ruby laser was realized. Experimental investigation and theoretical analysis indicate, the optimized pre-processing distorted the distribution of the electric field between gap′s electrodes, strengthened the effect of the Q-beam′s triggering, and ensured the chopped laser pulse with short duration and high power..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 465 (2007)
Design of a Dielectric-Metal-Dielectric Sandwich Structure for Efficient Side-Coupling of High Power Double-Clad Fiber Lasers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A novel dielectric-metal-dielectric sandwich structure based on the theory of sub-wavelength diffraction grating was presented for efficient side-coupling of high power double-clad fiber (DCF) lasers. The structure design considerations and simulation results with high coupling efficiency which can be over 80% were alsA novel dielectric-metal-dielectric sandwich structure based on the theory of sub-wavelength diffraction grating was presented for efficient side-coupling of high power double-clad fiber (DCF) lasers. The structure design considerations and simulation results with high coupling efficiency which can be over 80% were also presented. It can be used for high power laser diodes bar to side-pump DCF lasers without any beam-shaping. Besides, this side-coupling technique was scalable by multi-point pumping with several laser diodes bars..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 470 (2007)
Temporal Characteristics of the Gain-Switched Microchip Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Based on the rate equation, a mathematic model of laser diode (LD) pumped gain-switched Nd:YVO4 microchip laser under pre-pumping together with pulse pumping mechanism is presented. This model well shows the temporal characteristics of output pulses when the pumping parameters vary slightly. The results of numerical siBased on the rate equation, a mathematic model of laser diode (LD) pumped gain-switched Nd:YVO4 microchip laser under pre-pumping together with pulse pumping mechanism is presented. This model well shows the temporal characteristics of output pulses when the pumping parameters vary slightly. The results of numerical simulation indicate that the width of the output pulses changes little when the increase of pumping parameters is below 10%, however, the number of the output pulses increases rapidly and has a nonlinear monotone increasing relation with the pumping parameters. The experimental results of such gain-switched microchip laser are measured under the corresponding pumping conditions. It is found that the numerical and experimental results match with each other very well..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 475 (2007)
A Method for Improving the Performance of Ring Laser Gyro by Injecting the Multi-Cycles Step Noise with White Noise
[in Chinese], [in Chinese], and [in Chinese]
Based on the accumulation of lock-in error, a method for eliminating the dynamic lock-in error by injecting multi-cycles step noise with white noise into the mechanically dithered ring laser gyroscope (RLG) is presented. The theoretical analysis proves that the multi-cycles step noise enhances the bias stability of RLGBased on the accumulation of lock-in error, a method for eliminating the dynamic lock-in error by injecting multi-cycles step noise with white noise into the mechanically dithered ring laser gyroscope (RLG) is presented. The theoretical analysis proves that the multi-cycles step noise enhances the bias stability of RLG, as well as some intensity of the Gaussian white noise can reduce the accumulation of lock-in error during the step periods. The simulation experiment results show that this approach is prior to the traditional method in this way. Both methods decrease the bias error to the same orders of magnitude, while the bias stability is improved two or four times by injecting the multi-cycles step noise with white noise..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 481 (2007)
Passively Q-Switched Intracavity Optical Parametric Oscillator with Corner-Cube Resonator
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The theory of the non-critical phase-matched KTPⅡcrystal placed in corner-cube resonator was discussed. It was found that there existed eigen mode of special polarization azimuth to meet the non-eritical phase-matched condition. Experiment based on Cr4+:YAG passively Q-switched intracavity optical parametric oscillatorThe theory of the non-critical phase-matched KTPⅡcrystal placed in corner-cube resonator was discussed. It was found that there existed eigen mode of special polarization azimuth to meet the non-eritical phase-matched condition. Experiment based on Cr4+:YAG passively Q-switched intracavity optical parametric oscillator (OPO) was performed, and the conversion efficiency was higher than that in the plane-parallel resonator. The effects of the transmission of Cr4+:YAG crystal upon the intracavity power density were analyzed, and the relationship of signal-pulse energy versus pump energy with different transmission of Cr4+:YAG crystal was obtained. The performance of OPO laser was much better than that in plane-parallel resonator for the electro-optical efficiency can be up to 0.25%. A compact and efficient OPO was designed, the pump energy threshold was 4.7 J, the pulse energy was 11.8 mJ, the pulse width was 6.9 ns, the beam divergence was 7 mrad and the pulse stability was 5%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 485 (2007)
Biomedical Photonics and Laser Medicine
Using Spatially Resolved Reflectance to Measure Optical Properties of Stomach Tissue
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The optical properties and differences for normal human stomach mucosa/submucosa tissues in vitro at 488 nm, 514.5 nm, 532 nm, 630 nm and 632.8 nm wavelengths of laser were determined in this paper. Measurements were performed using a charge coupled device (CCD) detector, and optical properties were assessed from the mThe optical properties and differences for normal human stomach mucosa/submucosa tissues in vitro at 488 nm, 514.5 nm, 532 nm, 630 nm and 632.8 nm wavelengths of laser were determined in this paper. Measurements were performed using a charge coupled device (CCD) detector, and optical properties were assessed from the measurements using the spatially resolved reflectance, and nonlinear fitting of diffusion equation. The results of measurement showed that absorption coefficients, reduced scattering coefficients, optical penetration depths, diffusion constants, diffuse reflectance and shifts of the diffuse reflectance of the tissue samples at five different laser wavelengths vary with a change of laser wavelength. The maximum absorption coefficient for tissue samples is 0.482 mm-1 at 532 nm, and the minimum absorption coefficient is 0.224 mm-1 at 632.8 nm; the maximum difference in the absorption coefficients is 115% between 532 nm and 632.8 nm, and the minimum difference is 1.90% between 488 nm and 532 nm. The maximum reduced scattering coefficient for tissue samples is 5.93 mm-1 at 488 nm, and the minimum reduced scattering coefficient is 3.87 mm-1 at 632.8 nm; the maximum difference in the reduced scattering coefficients is 53.2% between 488 nm and 632.8 nm, and the minimum difference is 3.25% between 514.5 nm and 532 nm. The maximum optical penetration depth for tissue samples is 0.612 mm at 632.8 nm, and the minimum optical penetration depth is 0.341 mm at 488 nm. The maximum diffusion constant for tissue samples is 0.084 mm at 632.8 nm, and the minimum diffusion constant is 0.055 mm at 488 nm. The maximum diffuse reflectance for tissue samples is 0.356 at 630 nm, and the minimum diffuse reflectance is 0.271 at 532 nm. The maximum shift of the diffuse reflectance of the oblique incidence for tissue samples is 0.153 mm at 632.8 nm, and the minimum shift of the diffuse reflectance of the oblique incidence is 0.100 mm at 488 nm. It is obvious that there were distinct differences in the optical parameters for normal human stomach mucosa/submucosa tissues at five different laser wavelengths..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 582 (2007)
Properties of Pure Titanium for Dental Implants Fabricated by Rapid Laser Forming
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In the present experiments,pure titanium specimens fabricated by laser rapid forming (LRF) have been investigated, and based on the national standards (GB/T 13810-1997, GB/T 16886.5-2002), the mechanics properties, microstructure and cytotoxicity experiments were tested. The results show that tensile strength is 475 MPIn the present experiments,pure titanium specimens fabricated by laser rapid forming (LRF) have been investigated, and based on the national standards (GB/T 13810-1997, GB/T 16886.5-2002), the mechanics properties, microstructure and cytotoxicity experiments were tested. The results show that tensile strength is 475 MPa, yield strength is 383 MPa, elongation is 27%, Vickers hardness is 188.4～206.3, and Young′s modulus is 97.54 GPa. In vitro experiment, the cytotoxicity of LRF titanium specimens is grade 0. These data confirm that the LRF pure titanium can be efficient for surgical implants..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 588 (2007)
Laser Manufacturing
Identification of Different Laser Welding Penetration States Based on Multi-Sensor Fusion
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In order to classify typical penetration states in laser welding process, multi-sensors are applied to acquire the audible sound, ultraviolet and infrared (IR) emission signals, also penetration-state-relating features of each signal are extracted. Based on feature-level information fusion, simulated annealing algorithIn order to classify typical penetration states in laser welding process, multi-sensors are applied to acquire the audible sound, ultraviolet and infrared (IR) emission signals, also penetration-state-relating features of each signal are extracted. Based on feature-level information fusion, simulated annealing algorithm is utilized to optimize charactristic signals, consequently setting the “coeffients of feature fusion”. Pattern classifier is designed using back propagation (BP) network. It is found that through samples training and optimizing, a classification of 88%～100% has been made for detection of the four distinct penetration states such as “excessive penetration”, “full penetration”, “unstable penetration”, and “partial penetration”. So, an effective method for on-line monitoring for laser welding quality is provided..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 538 (2007)
Laser Cutting Special Steel Sheet Controlled by Rotating Gas Flow
[in Chinese], [in Chinese], and [in Chinese]
It is easy to produce molten slag by using traditional laser cutting technology in laser cutting some special steel such as stainless steel and so on. The main reason is that oxidizing reaction will take place inevitably by using oxygen as aided gas. So high pressure and high purity N2 or inert gases are used as aided It is easy to produce molten slag by using traditional laser cutting technology in laser cutting some special steel such as stainless steel and so on. The main reason is that oxidizing reaction will take place inevitably by using oxygen as aided gas. So high pressure and high purity N2 or inert gases are used as aided cutting gas in laser cutting stainless steel. After study of the forming principle and the rule of molten slag, a fine new laser cutting technology by using cyclone slag separator that will form rotating gas flow to control the direction of the flowing slag gas and oxygen as aided gas is presented. The experiments prove that by controlling the technical parameter reasonably, this laser cutting technology is practical and feasible. When the coaxial aided cutting gas is oxygen and the gas pressure is 300 kPa, the cyclone slag separator gas pressure is 100 kPa, the laser is TEM01and the output power is 500 W, the focal position is on the workpiece, and the cutting speed is 3 m/min, lubricous and dross-free cutting kerfs are obtained..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 543 (2007)
Microstructure and Wear Behaviour of Laser-Clad Zr-Cu-Ni-Al/TiC Composites on AZ91D Magnesium Alloy
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
To improve the wear property of magnesium alloy, wear-resistant TiC and in-situ ZrC co-reinforced Zr-based amorphous composite coating can be fabricated on AZ91D magnesium alloy by laser cladding using mixed powders Zr-Cu-Ni-Al/TiC. The microstructure of the coating was characterized by X-ray diffraction (XRD) and scanTo improve the wear property of magnesium alloy, wear-resistant TiC and in-situ ZrC co-reinforced Zr-based amorphous composite coating can be fabricated on AZ91D magnesium alloy by laser cladding using mixed powders Zr-Cu-Ni-Al/TiC. The microstructure of the coating was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The wear resistance of the coating was evaluated under dry sliding wear test condition at room temperature. The results show that the coating mainly consists of amorphous and different intermetallic phases. The coating exhibits excellent wear resistance due to the recombination action of amorphous and intermetallic compounds. And the wear resistance was improved further with the increase of TiC content. The main wear mechanism of the coating and the AZ91D sample are different, the former is fatigue peeling and adhesive wear and the latter is abrasive wear..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 549 (2007)
Size-Dispersal of Si Nanoparticles Prepared by Pulsed Laser Ablation
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A new method dispersed Si nanoparticles in the process of pulsed laser ablation (PLA) was proposed in this paper. A single crystalline Si target with high resistivity of 3000 Ω·cm was ablated by a XeCl excimer laser (wavelength: 308 nm, laser fluence: 3 J/cm2) in high-pure Ar gas at the ambient pressure of 10 Pa, A new method dispersed Si nanoparticles in the process of pulsed laser ablation (PLA) was proposed in this paper. A single crystalline Si target with high resistivity of 3000 Ω·cm was ablated by a XeCl excimer laser (wavelength: 308 nm, laser fluence: 3 J/cm2) in high-pure Ar gas at the ambient pressure of 10 Pa, and the Si nanoparticles were systemically deposited on glass or single crystalline Si substrates located at a distance of 2.0 cm under the plume. The Raman spectra indicate that Si nanoparticles were obtained in the samples at different horizontal distances, 0.5～2.8 cm, from Si target. The scanning electron microscopy (SEM) images show that the average size of Si nanoparticles gradually decreased with increasing the distance from the target. The experimental results were explained by ablation dynamics. Because Si nanoparticles with different masses gained the different horizontal velocity, Si nanoparticles were dispersed according to their sizes under gravitation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 555 (2007)
Microstructure and Wear Resistance of a Laser Melting-Deposited γ/NiMo Near-Eutectic Alloy
[in Chinese], and [in Chinese]
A γ/NiMo near-eutectic alloy mainly consisting of NiMo intermetallic compound and Ni-based solid solution γ was fabricated by laser melting deposition process using Ni-Mo elemental powder blends. Microstructure and room temperature dry sliding wear resistance of the alloy at different sliding speeds and test loads wereA γ/NiMo near-eutectic alloy mainly consisting of NiMo intermetallic compound and Ni-based solid solution γ was fabricated by laser melting deposition process using Ni-Mo elemental powder blends. Microstructure and room temperature dry sliding wear resistance of the alloy at different sliding speeds and test loads were studied. The alloy has a homogeneous microstructure and better wear resistance even at higher sliding speed and test load. Wear volume loss of the alloy is extremely insensitive to increasing wear test load at each sliding speed while coefficient of friction drastically decreases with the increase of both sliding speed and test load, what′s more, higher sliding speed brings lower wear volume loss and lower coefficient of friction, which is dominantly due to the combination of high hardness of the NiMo intermetallic compound and good toughness of the Ni-based solid solution γ. Wear volume loss of the alloy is only ten percent of that of hardened 0.45% C steel under the same testing condition of 0.93 m/s sliding speed and 196 N test load..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 559 (2007)
Modelling of the Keyhole Formation under High Intensity Laser Power
[in Chinese], [in Chinese], and [in Chinese]
Keyhole effect is one of the characteristics during deep penetration laser welding. Laser keyhole results in obvious improvement of the coupling efficiency of laser power in the metal sheet. The laser energy attenuation along the thickness of the sheet occurs due to the inverse bremsstrahlung absorption inside the keyhKeyhole effect is one of the characteristics during deep penetration laser welding. Laser keyhole results in obvious improvement of the coupling efficiency of laser power in the metal sheet. The laser energy attenuation along the thickness of the sheet occurs due to the inverse bremsstrahlung absorption inside the keyhole. On the other hand, the keyhole plasma plays welding heat source role in transferring laser energy to melt pool. As a result, a combination of a rotary volumetric heat source with a double ellipsoid volumetric heat source was proposed, and the governing equations consisting of mass conservation, momentum conservation and energy conservation for the incompressible fluid flow and heat transfer are solved using SIMPLE algorithm based on control volume method. Influence of weld process parameters on the keyhole dimensions was simulated. In addition, validation experiments were carried out in order to compare weld shape and its size..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 564 (2007)
High Power CO2Laser Brazing of Diamond Grits
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
High power transverse flow CO2 laser was used to scan the brazing alloy and diamond grits. The influence of laser technological parameters on brazing layer combination performance and diamond grits thermal damage was researched, and the thermal damage mechanism of laser brazed diamond and the combination mechanism of bHigh power transverse flow CO2 laser was used to scan the brazing alloy and diamond grits. The influence of laser technological parameters on brazing layer combination performance and diamond grits thermal damage was researched, and the thermal damage mechanism of laser brazed diamond and the combination mechanism of brazing layer and diamond grits were analyzed. The research results showed that laser power and scanning speed were the main factors for diamond thermal damage and surface wetting. On the conditions of 0.5 mm brazing layer thickness, argon shield, 800 W laser power, and 8.39 mm/s scanning speed, the best combination performance among the diamond grits, brazing alloy and metallic base can be achieved. Brazing alloy wetted the diamond grits well and reacted with them to form TiC and SiC. Under high laser energy input, oxidation take placed between diamond grits and oxygen outside, diamond would be oxidized all along on the condition of branch gas pressure about free equation until the balance established between diamond and oxide, during this process, diamond grits would be carbonized or burn out and gasified..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 569 (2007)
Processing of Laser Quenching Crankshaft
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
It aims to realize the laser quenching and cladding for the principle axis and crank of single or more crank while the crankshaft is laid horizontally and rotating around the principal axis. The track of the laser spot is deduced when the laser acts on the surface of the crank and forms whorl line. According to the motIt aims to realize the laser quenching and cladding for the principle axis and crank of single or more crank while the crankshaft is laid horizontally and rotating around the principal axis. The track of the laser spot is deduced when the laser acts on the surface of the crank and forms whorl line. According to the motion characteristic of 802D numerically-controlled machine tool in four axes linkage generally used for laser quenching, with the arc interpolation method, the numerically controlled programme for laser net veins quenching is made in the form of four axes linkage. With this, the net veins laser quenching and surface cladding for crankshaft are accomplished on the four axes linkage laser machine tool, when the crankshaft is laid horizontally and rotating around the principal axis. Because the principal axis is rotating at a constant speed, no balance iron is needed to locate the workpiece, the work process is steady, only one time of location is needed, and no more movement of the rotating axis is needed to accomplish laser quenching and cladding of the crankshaft with single or more cranks, which puts the ability of the above machine tool for laser quenching to good use..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 574 (2007)
Laser Induced Breakdown Spectroscopy of the Trace Metal Element Pb in Soil
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The laser induced breakdown spectroscopy (LIBS) spectra of the soil are measured in the visible spectral region. The main and some trace elements of the soil sample are obtained by the analysis and assignment of spectral structure and spectral lines respectively. Additionally, the intensities of Pb 405.78 nm spectral lThe laser induced breakdown spectroscopy (LIBS) spectra of the soil are measured in the visible spectral region. The main and some trace elements of the soil sample are obtained by the analysis and assignment of spectral structure and spectral lines respectively. Additionally, the intensities of Pb 405.78 nm spectral line are measured at the different concentration of Pb in soil. The LIBS calibration curve of the analytical spectral line is obtained by internal calibration, and the value of detection limit, 36.7×10-6, is obtained from the fit of the calibration curve..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 577 (2007)
Laser Physics
Proper Orthogonal Decomposition and Low Dimensional Approximation of Aero-Optical Aberrated Wavefronts
[in Chinese], and [in Chinese]
The aero-optical aberrated wavefronts are measured by applying Hartmann wavefront sensor when the collimated parallel beam passes through a low speed heated turbulent jet. Proper orthogonal decomposition (POD) and the low dimensional approximation are applied to the aberrated wavefront time series, the comparisons betwThe aero-optical aberrated wavefronts are measured by applying Hartmann wavefront sensor when the collimated parallel beam passes through a low speed heated turbulent jet. Proper orthogonal decomposition (POD) and the low dimensional approximation are applied to the aberrated wavefront time series, the comparisons between the measured wavefronts and low dimensional approximation reconstruction wavefronts of 16# and 1008# were conducted. The results indicated that the aberrated wavefronts can be expanded by the POD group and can be described with a few POD modes, with the more the reconstruction modes the more the reconstruction precision. Due to the difference of the spacial correlation of phase pulsating quantity at different wavefront positions, the reconstruction precision different data points is not same for the same reconstruction modes..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 491 (2007)
Higher-Order Mode Method for Improving Line Intensity Uniformity of Laser Beam Line Generator
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Aimed at un-uniform line intensity of laser beam line generator caused by Gaussian distribution of based mode intensity, a new method replacing the based mode with higher-order mode such as TEM20, TEM40 was presented in this paper. The intensity distribution at one of the orthogonal directions of such higher-order modeAimed at un-uniform line intensity of laser beam line generator caused by Gaussian distribution of based mode intensity, a new method replacing the based mode with higher-order mode such as TEM20, TEM40 was presented in this paper. The intensity distribution at one of the orthogonal directions of such higher-order mode is the overlapping of several Gaussian distributions. It is more even than single Gaussian intensity distribution of based mode. More short the distance between the near Gaussian apices, more even the intensity distribution of the higher-order mode. The higher-order modes were got by moving transversely laser diode (LD) apart from the axis of the resonator in the experiment. The distance between the near Gaussian apices is controlled accurately by controlling accurately the divergence of LD. At 1 m working distance of laser beam line generator, the data of line intensity were obtained when based mode and higher-order mode incidence acted as the source respectively. The data proved that the overlapping intensity distribution of higher-order mode could improve the line intensity uniformity..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 496 (2007)
Materials and Thin Films
Synthesis and Research of Photochromism Based on Side-Polyimide Containing Azobenzene Group
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The side polyimide containing azobenzene group was synthesized with photochromism property from 2,2-Bis (3-amino-4-hydroxyyphenyl) hexafluoropropane (6FHP), pyromellitic dianhydride (PMDA) and dispersed red 1 (DR1). The chemical structure and thermal properties of polyimide were characterized using Fourier transform inThe side polyimide containing azobenzene group was synthesized with photochromism property from 2,2-Bis (3-amino-4-hydroxyyphenyl) hexafluoropropane (6FHP), pyromellitic dianhydride (PMDA) and dispersed red 1 (DR1). The chemical structure and thermal properties of polyimide were characterized using Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy, differential scanning calorimeter (DSC), and thermal gravimetric analysis (TGA). The DSC and TGA exhibited the glass transition temperature (Tg) and the decomposition temperature (Td) of polymer were 298 ℃ and 365 ℃, respectively. These results showed that the material had excellent thermal stability. The UV-induced trans/ cis photoisomerization and the thermal reflex-isomerization behavior were investigated for the polymer in solution and in film. The results indicate that the polymer solution and polymer film can undergo photochromism after a given UV wavelength (365 nm) photoinduction. This showed that the polyimide could be used to carry out perpetuity photoinduced birefringence and recording..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 525 (2007)
Working Mechanism of the Binary Eutectic Alloy Mask Layer in Super-Resolution Near-Field Structure
[in Chinese], [in Chinese], and [in Chinese]
Super resolution near-field structure (super-RENS) is one of the most promising candidates for the ultrahigh-density optical storage, and near-field optical properties of the mask layer in super-RENS optical disk are crucial for its optical storage performance. The near-field distribution through the eutectic alloy masSuper resolution near-field structure (super-RENS) is one of the most promising candidates for the ultrahigh-density optical storage, and near-field optical properties of the mask layer in super-RENS optical disk are crucial for its optical storage performance. The near-field distribution through the eutectic alloy mask layer has been studied by using three-dimensional finite-difference time-domain (3D-FDTD) method. Simulation results indicate that the periodic micro-/nano-structures formed in the eutectic binary alloy films after or during irradiation of a laser beam will result in a prominent near field enhancement and may be the origin of the higher signal-to-noise ratio (SNR) in super-RENS optical disk..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 530 (2007)
Preparation of ZnO Thin Films by Pulsed Laser Deposition
[in Chinese], and [in Chinese]
ZnO thin films, as novel materials for Ⅱ-Ⅵ semiconductors, have excellent microstructural, optical and electronic properties. Ultraviolet (UV) stimulated emission is an outstanding merit of ZnO thin films. Nanostructured ZnO films with grain size of 28～35 nm have been prepared on quartz glass substrates by pulse laser ZnO thin films, as novel materials for Ⅱ-Ⅵ semiconductors, have excellent microstructural, optical and electronic properties. Ultraviolet (UV) stimulated emission is an outstanding merit of ZnO thin films. Nanostructured ZnO films with grain size of 28～35 nm have been prepared on quartz glass substrates by pulse laser ablation of Zn target in oxygen atmosphere. The structural and optical properties of the films were studied. ZnO thin films with typical c-axis (002) orientation were successfully deposited at a range of 100～250 ℃. The results obtained by X-ray diffraction (XRD) and photoluminescence (PL) measurements show that the strong UV emission centering is about 378～385 nm and deep-level emission centering about 518～558 nm in the room temperature PL spectra of the ZnO films. It is noteworthy that only strong UV emission (without deep-level emission) was obtained from ZnO film deposited at the substrate temperature of 200 ℃. This was attributed to its best crystallization..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 534 (2007)
Measurement and Metrology
Detection of a Sound of Modulation Signal in Scattering Laser
[in Chinese], [in Chinese], and [in Chinese]
Based on a scattering laser principle of photoelectricity sounding from the target, a infrared laser is used in detecting sound wave. On the foundation of researching target specific feature and estimated scattering laser power of echo signal, the experimental equipment is designed. In experiment, a sound of modulationBased on a scattering laser principle of photoelectricity sounding from the target, a infrared laser is used in detecting sound wave. On the foundation of researching target specific feature and estimated scattering laser power of echo signal, the experimental equipment is designed. In experiment, a sound of modulation signal is detected from glass target in scattering infrared laser. If the distance between target and light source was 6～63 m and the reflection of laser ray is β≤±4° (an angle with the detector spool) the sound of echoic modulation signal should be heard. If β=4°～15°, the echo signal of scattering laser can be detected, but the sound cannot be heard. Experiment proves that the method of sounding sound wave using scattering laser from the target is feasible..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 507 (2007)
Dynamic Thermal Abberation Measurement of Side-Pumped Slab Laser Medium
[in Chinese], [in Chinese], and [in Chinese]
Based on the measurement theory of laser medium thermal abberation with interference fringe, a method is proposed to measure the dynamic thermal abberation of slab laser medium. The interference fringe is recorded by charge coupled device (CCD) cameral and then processed by computer. With analysis of the interference fBased on the measurement theory of laser medium thermal abberation with interference fringe, a method is proposed to measure the dynamic thermal abberation of slab laser medium. The interference fringe is recorded by charge coupled device (CCD) cameral and then processed by computer. With analysis of the interference fringe, a simple and rapid algorithm to extract the center of interference fringe is proposed. The dynamic thermal abberation of slab laser medium in pumping process by analyzing and calculating the movement of interference fringes is obtained, which paves the way to dynamically compensating the thermal effect of the laser medium. In experiments, N31 phosphate laser glass is used as the sample, and the interior temperature distribution during heating procedure is obtained. The relative error is about 3%, and the validity of the method is proved..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 511 (2007)
Wavefront Measurement for Transparent Object by Active Deflectometry
[in Chinese], [in Chinese], and [in Chinese]
A new wavefront measurement was proposed, which was based on active deflectormetry and phase-shift technique. The deflection of imaging rays caused by a phase object could be measured accurately with the phase-shift technique and a removable screen displaying the horizontal and vertical sinusoidal intensity patterns reA new wavefront measurement was proposed, which was based on active deflectormetry and phase-shift technique. The deflection of imaging rays caused by a phase object could be measured accurately with the phase-shift technique and a removable screen displaying the horizontal and vertical sinusoidal intensity patterns respectively, and then the wavefront distribution could be calculated after extracting the gradients from the deflection. When a phase object was placed between a screen and a calibrated charge coupled device (CCD) camera, the intensity patterns would be distorted. The distortion distribution can be measured, and another different distortion distribution can be got by moving the screen. Therefore the ray deflection and the wavefront can be obtained. The experimental results of a positive lens had confirmed the feasibility of this method..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 515 (2007)
Non-Flatness Measurement of Wafer Stage Mirrors in a Step-and-Scan Lithographic Tool
[in Chinese], [in Chinese], and [in Chinese]
A novel in-situ non-flatness measurement method of wafer stage mirrors in a step-and scan lithographic tool is presented. According to the impact of mirror non-flatness on wafer stage′s positioning, the non-flatness of the mirror is expressed as translation compensation and rotation compensation usually. The double freA novel in-situ non-flatness measurement method of wafer stage mirrors in a step-and scan lithographic tool is presented. According to the impact of mirror non-flatness on wafer stage′s positioning, the non-flatness of the mirror is expressed as translation compensation and rotation compensation usually. The double frequency laser interferometers are used to measure the horizontal positions and rotations of the wafer stage. The whole measurement is divided into several sequences. Each sequence includes a whole measurement of the valid area of the mirror. The rotation compensation of the mirror is calculated from each measured values of the wafer stage′s rotation. The coarse translation compensation of the mirror is calculated recursively by setting a temporary boundary condition in each sequence. The cubic spline interpolation method and least square method are used to smooth and connect all the coarse translation compensations of the mirror to calculate the accurate translation compensation of the mirror. Experiment results prove that by this method the measurement reproducibility of the translation compensation of mirror is better than 2.957 nm and the measurement reproducibility of the rotation compensation of mirror is better than 0.102 μrad..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 519 (2007)
Optical Communication
Control of Bit Error Rate Introduced by Platform Vibration for Free Space Optical Communication
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
For free space optical communication (FSO), various stochastic interfering factors make the communication platform oscillate, as a result the original collimated link is broken, and the bit error rate (BER) increases. For the purpose of reducing BER, the method of controlling the optical spot's shape and size on thFor free space optical communication (FSO), various stochastic interfering factors make the communication platform oscillate, as a result the original collimated link is broken, and the bit error rate (BER) increases. For the purpose of reducing BER, the method of controlling the optical spot's shape and size on the receiving end is given, also the principle of obtaining a certain optical spot via astigmatism and the design example are presented in this paper. The result indicates that the BER introduced by vibration could be reduced to the minimum while choosing the optical pot parameters on the receiving end via adjusting the transmitting optical antenna. For the situation of dissymmetry oscillation, the optical spot should be ellipse..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 499 (2007)
Reviews
New Progress and Prospect of Realistic Image Rendition Based on Visual Characteristics
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Visual characteristics have been successfully applied to the study of realistic image rendition, which may provide higher quality images for human observation and machine vision. At first, the latest main researches on visual characteristics are briefly summarized, including visual spatial opponent, spectral opponent, Visual characteristics have been successfully applied to the study of realistic image rendition, which may provide higher quality images for human observation and machine vision. At first, the latest main researches on visual characteristics are briefly summarized, including visual spatial opponent, spectral opponent, visual adaptation, and visual cortex primary processing and so on. The development of realistic image rendition techniques based on visual characteristics is summarized in this paper. Since various algorithms have different emphases, the Retinex family methods primarily focusing on keeping color constancy and some other methods aiming at getting high dynamic range compression are analyzed in detail. Our study on this field is also mentioned and compared with some excellent algorithms according to theory structure and experiment results. Related representative software and hardware realization techniques are introduced, and our next research direction and the prospect on this field are given..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 4, 451 (2007)
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